SPRING-BACK PREDICTION OF MILD STEEL SHEET ON 60º AIR BENDING MOHD ZUHAIRI BIN MD ZOHIR

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1 SPRING-BACK PREDICTION OF MILD STEEL SHEET ON 60º AIR BENDING MOHD ZUHAIRI BIN MD ZOHIR Report submitted in fulfilment of The requirements for the award of the degree of Bachelor of Mechanical Engineering Faculty of Mechanical Engineering UNIVERSITI MALAYSIA PAHANG DECEMBER 2010

2 ii UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING I certify that the project entitled Spring-back prediction of mild steel sheet on 60º air bending is written by Mohd Zuhairi Bin Md Zohir. I have examined the final copy of this project and in our opinion; it is fully adequate in terms of scope and quality for the award of the degree of Bachelor of Engineering. I herewith recommend that it be accepted in partial fulfilment of the requirements for the degree of Bachelor of Mechanical Engineering. Examiner Signature

3 iii SUPERVISOR S DECLARATION I hereby declare that I have checked this project and in my opinion, this project is adequate in terms of scope and quality for the award of the degree of Bachelor of Mechanical Engineering. Signature: Name of Supervisor: JASRI MOHAMAD Position: LECTURER OF MECHANICAL ENGINEERING Date: 6 DICEMBER 2010

4 iv STUDENT S DECLARATION I hereby declare that the work in this project is my own except for quotations and summaries which have been duly acknowledged. The project has not been accepted for any degree and is not concurently submitted for award of other degree. Signature: Name: MOHD ZUHAIRI BIN MD ZOHIR ID Number: MA07059 Date: 6 DICEMBER 2010

5 vi ACKNOWLEDGEMENTS I am grateful and would like to express my sincere gratitude to my supervisor Mr. Jasri Mohamad for his germinal ideas, invaluable guidance, continuous encouragement and constant support in making this research possible. He has always impressed me with his outstanding professional conduct, his strong conviction for science, and his belief that a bachelor program is only a start of a life-long learning experience. I appreciate his consistent support from the first day I applied to graduate program to these concluding moments. I am truly grateful for his progressive vision about my training in science, his tolerance of my naive mistakes, and his commitment to my future career My sincere thanks go to all my labmates and members of the staff of the Mechanical Engineering Department, UMP, who helped me in many ways and made my stay at UMP pleasant and unforgettable. I acknowledge my sincere indebtedness and gratitude to my parents for their love, dream and sacrifice throughout my life. I acknowledge the sincerity of my parentsin-law, who consistently encouraged me to carry on my higher studies in Malaysia. I cannot find the appropriate words that could properly describe my appreciation for their devotion, support and faith in my ability to attain my goals. Special thanks should be given to my committee members. I would like to acknowledge their comments and suggestions, which was crucial for the successful completion of this study.

6 vii ABSTRACT This report deals with the deformation of a spring-back on 60 air bending. Now days, many research and study have been done on a spring-back. In sheet metal bending, a flat part is bent using a set of punches and dies. In this thesis, punches and die are referred to as tools. The punch and the dies are mounted on a press brake, which control the relative motion between the punch and die and provides the necessary bending pressure. In this thesis, the spring-back is done by using both experimental and simulation using FEA software which is ABAQUS 6.7. The material use in this project is mild steel with 1 mm thickness. The size of the specimen is 100 mm x 100 mm. The experimental is done fist follow by the simulation. The specimen required in this project is 10 specimens. The Profile Projector machine is use to measure the angle of the sheet metal in the experiment. In the simulation, 2D drawing of the model have been made using ABAQUS 6.7. The punch, die and the sheet metal is main part in the drawing. The sheet metal then is defined as a rigid body in the software. The meshing has been done to sheet metal with 0.5 mm of the mesh size. After all the simulation is done, several node has been taken to measure the angle by using AutoCAD software. 8 nodes is taken an then transfer it to the AutoCAD software. The result from both experimental and simulation then be compared. The spring-back value in experimental is 62.3 while in the simulation the value is 62.

7 viii ABSTRAK Laporan ini berkaitan fenomena spring-back yang berlaku pada 60 pembengkokkan secara tergantung. Dewasa ini, banyak kajian telah dilakukan pada spring-back. Dalam lembaran logam membengkok, bahagian datar akan di bengkokkan menggunakan satu set pemukul dan acuan. Dalam tesis ini, pemukul dan acuan disebut sebagai alat. Pemukul dan acuan sudah dipasang pada mesin, yang mengendalikan gerakan relatif antara pemukul dan acuan dan memberikan tekanan membengkokkan diperlukan. Dalam tesis ini, fenomena spring-back dilakukan dengan menggunakan perisian FEA dan eksperimen. Perisian yang digunakan adalah ABAQUS 6,7. Bahan yang digunakan dalam projek ini adalah kepingan besi dengan ketebalan 1 mm. Saiz spesimen adalah 100 mm x 100 mm. Spesimen yang diperlukan dalam projek ini adalah 10 spesimen. Mesin Profile Projector digunakan untuk mengukur sudut lembaran logam. Dalam simulasi, 2D gambar model telah dibuat dengan menggunakan ABAQUS 6.7. Pemukul, acuan dan lembaran logam adalah bahagian utama dalam gambar. Logam lembaran kemudian ditakrifkan sebagai benda tegar dalam perisian. Meshing telah dilakukan untuk kepingan logam dengan 0,5 mm saiz mesh. Setelah semua simulasi dilakukan, beberapa node telah diambil untuk mengukur sudut dengan menggunakan perisian AutoCAD. 8 node telah diambil kemudian dipindah ke perisian AutoCAD. Keputusan daripada kedua-dua percubaan dan simulasi kemudian akan dibandingkan. Nilai spring-back dalam eksperimen adalah 62,3 manakal pada simulasi pula nilai adalah 62.

8 ix TABLE OF CONTENTS SUPERVISOR S DECLARATION STUDENT S DECLARATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS LIST OF ABBREVIATIONS Page iii iv vi vii viii ix xii xiii xv xvi CHAPTER 1 INTRODUCTION 1.1 Introduction Project Background Bending Principle Problem Statement Project Objective Scope of the Project 3 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction Theory of Sheet Metal Common Types of Bending V-Bending U-Bending Wiping Die Bending (L-Bending) Bend Allowance Air Bending 10

9 x 2.6 Spring-Back V-Bending Compensation for Spring-Back Material Low Carbon Steel Previous Study of Spring-Back in V-Bending An experimental study on the examination of spring-back with several thickness and properties in bending dies Determining spring-back amount of steel sheet metal has 0.5 mm thickness in bending dies CHAPTER 3 METHODOLOGY 3.1 Introduction Flow Chart Simulation Material Properties Elastic Properties Plastic Properties Material Modelling Experimental Mechanical Drawing Bending Machine Material Process 30 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Introduction FEA Result Analysis Experimental Result Result Summary 38 CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 5.1 Introduction Conclusion Recommendation 39

10 xi REFERENCES 41 APPENDICES 42 A Gantt chart for Final Year Project 1 42 B Gantt chart for Final Year Project 2 43

11 xii LIST OF TABLES Table No. Title Page 2.1 Chemical composition of materials Bending angle of sheet metal 0.5 mm thickness (method 1) Bending angle of sheet metal 0.5 mm thickness (method 2) Low carbon steel carbon percentage and Young s Modulus Plastic properties data Lower die specification Upper punch specification Nodes number Experiment result of bending analysis Spring-back angle for experiment and simulation 38

12 xiii LIST OF FIGURES Figure No. Title Page 1.1 Beam Beam is flexed Diagram of V-bending Diagram of U-bending Diagram of L-bending Bend allowance Bend deduction Diagram of K-factor Diagram to calculate bend allowance using K-factor Diagram of air-bending Spring-back in bending Spring-back graph of 0.50 mm (method 1) Spring-back graph of 0.75 mm (method 1) Spring-back graph of 1.00 mm (method 1) Spring-back graph of 0.5 mm (method 2) Spring-back graph of 0.75 mm (method 2) Spring-back graph of 1.00 mm (method 2) Spring-back graphic of 0.5 mm steel sheet metal yielded by using the first method and yielded polynomial curve equation 2.17 Spring-back graphic of 0.5 mm steel sheet metal yielded by using the second method and yielded polynomial curve equation 2.18 Graphic were four methods are combined (bending angle vs spring-back angle) FEA modelling Stress-strain graph CAD drawing 28

13 xiv 3.4 TrumaBend V85S bending machine Plate press by punch Mitutoyo profile projector Punch press the plate Punch is released Node coordinate develop in CAD software V-bending specimen Angle measure using profile projector machine 37

14 xv LIST OF SYMBOL Y E α L t ν ε σ Actual radius Radius after spring-back Yield strength Elastic modulus Angular Total Flat Length Poisson Ratio Plastic Strain Yield Stress

15 xvi LIST OF ABBREVIATIONS FEA CAD BD BA 2D Finite Element Analysis Computer-aided Design Bend Deduction Bend Allowance 2 Dimension

16 CHAPTER 1 INTRODUCTION 1.1 INRODUCTION This chapter will discuss about the project background, problem state, project objective and the scope of the project. 1.2 PROJECT BACKGROUND In sheet metal bending, a flat part is bent using a set of punches and dies. In this thesis, punches and die are referred to as tools. The punch and the dies are mounted on a press brake, which control the relative motion between the punch and die and provides the necessary bending pressure Bending Principle Take a beam 1m long if it starts as a straight beam then the length measured along the top face with the aid of a tape measure is one meter. Similarly the bottom face will also be one meter as shown in Figure 1.1 below. A C 1m 1m B D Figure 1.1: Beam

17 2 When the beam was straight, AB was equal to CD, but mow by visual inspection it is now obvious that this is not the case, once the beam is flexed. The beam as shown is said to be hogging so that the upper face is longer than the bottom face as shown in Figure 1.2 below. A X C D Y B Figure 1.2: Beam is flexed If the beam is solid then there cannot be any migration of material from the bottom to the top reaches of the beam (because solids are generally rigid or semi-rigid). The only way the hogging can occur is if AB is stretched further than CD by the bending action. If AB remains 1m then CD must be shorter, the bottom face is therefore compressed and the fibres beneath the surface of the bottom face experience compressive stress. If however CD remains 1m then the upper face AB must have been stretched and the fibres beneath the upper surface are subject to tensile stress. The two conditions just described represent two extremes. In most flexing situations, reality is somewhere between the two and in many cases is close to halfway between the two, such that length XY midway between AB / CD remains 1m. Therefore AB is stretched and CD is compressed. The third situation is that assumed in the theory of simple bending generally used for analysis of bending and buckling.

18 3 1.3 PROBLEM STATEMENT Whenever forming metals, some spring-back occurs. The cause of this springback is the residual stress that is an inevitable result of cold working metals. For example, in a simple bend, residual compressive stress remains on the inside of the bend, while residual tensile stress is present on the outside radius of the bend. The most common method of correcting for spring-back is to overbend the material to obtain the desired shape after forming. Simply stated, in a bend, residual compressive stress remains on the inside of the bend, while residual tensile stress is present on the outside radius of the bend. 1.4 PROJECT OBJECTIVE The objectives of this study are: a) To evaluate and compare the most reliable material modeling in finite element analysis (FEA) predict in spring-back. b) To apply finite element analysis (FEA) technology in sheet metal forming of bending. 1.5 SCOPE OF THE PROJECT The scopes of the project are limited to: a) Develop 2D modeling of V-bending in Finite Element software b) Analyze 2D modeling Finite Element software purpose for spring-back. c) Conduct experiment for V-bending using bending machine (air bending). d) Analyze the simulation and experiment result. e) Compare the result from both tasks.

19 CHAPTER 2 LITERATURE REVIEW 2.1 INTRODUCTION In this chapter it will discuss about theory of the sheet metal, the common types of bending bend allowance, air bending, spring-back in v-bending, material, and some previous study in v bending. 2.2 THEORY OF SHEET METAL Sheet metal forming differs from other deformation processes such as rolling, hot extrusion and wire drawing in that it is a non-steady-state process. A deformation zone exists into which all the material enters and is subjected to a fixed deformation pattern before exiting while, in sheet metal forming, different deformation modes can operate in differ areas of the sheet or, subsequently, in the same area, initiated by the interaction between a contoured piece of sheet metal with shaped tools, which are usually installed in a power press. In sheet metal we can use it to bend. Not all sheet metal has a correct angle when it was bending. This phenomenon calls spring-back. Spring-back occur until residual stress forces are balanced by the material s stiffness. There is some factors that affect spring-back such as higher material strength, thinner material, lower young s modulus, larger die radius, greater wipe steel clearance, less irregularity in part outline and flatter part surface contour.

20 5 If a flanged part has a lot of irregularity in the flanged area and the part surface contour contributes to stiffness, the spring-back will be less. Large wiping-steel clearances can result in spring-back of several degrees or more. 2.3 COMMON TYPES OF BENDING There is several type of bending process used in industry. The common use is V- bending, U-bending and wiping dies bending (L-bending) V-bending In V-bending, the clearance between punch and die is constant (equal to the thickness of sheet blank). It is used widely. The thickness of the sheet ranges from approximately 0.5 mm to 25 mm. Figure 2.1: Diagram of V-bending process Source: Diegel, 2002

21 U-bending U-bending is performed when two parallel bending axes are produced in the same operation. A backing pad is used to force the sheet contacting with the punch bottom. It requires about 30% of the bending force for the pad to press the sheet contacting the punch. Figure 2.2: Diagram of U-bending process Source: Diegel, Wiping die bending (L-bending) Wiping die bending is also known as flanging. One edge of the sheet is bent to 90º while the other end is restrained by the material itself and by the force of blankholder and pad. The flange length can be easily changed and the bend angle can be controlled by the stroke position of the punch.

22 7 Figure 2.3: Diagram of L-Bending Source: Diegel, BEND ALLOWANCE When sheet metal is bent, the inside surface of the bend is compressed and the outer surface of the bend is stretched. Somewhere within the thickness of the metal lies its natural axis, which is a line in the metal that is neither compressed nor stretched. What this means in practical terms is that if we want a work piece with a 90º bend in which one leg measures A and other measures B, then the total length of the flat piece is not A+B. to work out what length of the flat piece of metal needs to be, we need to calculate the Bend Allowance or Bend Deduction that tells us how much we need to add or subtracts to our leg length to get exactly what we want.

23 8 Figure 2.4: Bend allowance L t = A + B + BA (2.1) Where: L t = total flat length BA = bend allowance value Figure 2.5: Bend deduction L t = A + B BD (2.2) Where: L t = total flat length BD = bend deduction value

24 9 The location of the neutral line varies depending on the material itself, the radius of the bend, the ambient temperature, direction on the material grain, and the method by which it is being bent, etc. the location of this line is often referred to as the K-factor. K-factor is a ratio that represents the location of the neutral sheet with respect to the thickness of the sheet metal part. Figure 2.6: Diagram of K-factor Source: Diegel, 2002 The only truly effective way of working out the correct bend allowance is to reverse engineer it by taking a measured strip of material, bending it and measuring it to calculate the bend allowance. These bend allowance can be measured for many materials and scenarios and then tabulated so that the table can be used by CAD programs to produce accurate sheet metal work. Many CAD programs however also work out bend allowances automatically by using K-factor calculations.

DESIGN ANALYSIS OF EXTERIOR CAR BODY PART BASTIAN WIBAR BIN MOMANG

DESIGN ANALYSIS OF EXTERIOR CAR BODY PART BASTIAN WIBAR BIN MOMANG Thesis submitted in partial fulfillment of the requirements for award of Bachelor of Mechanical Engineering with Automotive Engineering